1. Field of the Invention
The present invention relates to radio telephone systems and their control methods of multi-channel access type which detect an idle one of a plurality of radio channels and send or receive a voice or datum signal through the idle channel and, more particularly, to a cordless telephone system and its control method wherein a mobile unit is normally disposed in a predetermined positional relationship with a base unit connected to a wired line.
2. Description of the Related Art
A prior art cordless telephone system is arranged so that, when an incoming call arrives at a cordless telephone, a user can talk with the party by operating a hook switch provided within the dial unit of the radio telephone set. Accordingly, if there is an incoming call at the radio telephone set mounted on the telephone-set receiving part of the base unit, then the user must first pick up the readio telephone set from the set receiving part of the base unit and then operate the hook switch of the telephone set. This radio telephone set, when compared with an ordinary home telephone set through which the user can talk with the party only by lifting the handset of the telephone set, is very troublesome in handling. The same explanation also holds true when the user wishes to end the conversation. This leads to the fact that, when the user frequently uses the telephone, such handling becomes highly inconvenient.
Another problem of the prior art cordless telephone system is that the mobile unit must be continuously or intermittently powered by a battery to detect a control signal transmitted from the base unit in response to the arrival of an incoming call. Similarly, the base unit must be powered by a battery or a commercial power source to detect a control signal transmitted from the mobile unit in response to a user's operation for a call origination. Thus, power is consumed so much to monitor the control signals. Especially, the consumption of battery power is a more serious problem to the mobile unit because it has only a limited power capacity.